In higher speed line printing, it has been found that the band or belt type printer has certain advantages over the drum type printer. The band is caused to be driven in continuous manner along a line of printing wherein a plurality of hammers are aligned to be selectively driven into impact with record media and an associated ribbon against type characters on the print band. Since it is desired to control the speed of the print band within close tolerances so as to permit driving of the hammers into proper registration with the characters on the print band, the band speed is an important aspect of the printer. The prior art has utilized timing marks on the band, and timing pulses derived from such marks on the print band have served to control the speed of the band by means of servo motor control. Synchronous A.C. motors have also been used to drive the type bands.
Additionally, it is well known that a type or character band includes a plurality of font sets wherein each character of every font set is continuously scanned by the control apparatus so as to fire the selected hammers at the precise time that the characters pass the various print positions. The band may include marks thereon which correspond to the characters and may also include marks to indicate the various font sets with sensing or detecting means being provided to send pulses to the control mechanism at precise times for firing the hammers.
Another feature of a band printer includes the providing of hammers wherein a separate hammer is provided for each print position with a hammer driver for each hammer. Other band printers have utilized timeshared hammer techniques wherein the hammers are of multi-width and span more than one print column position, or single width hammers which are movable to more than one print position and are arranged in a bank with such bank being movable or displaced along a line of printing.
The print band usually has the characters etched, engraved, embossed or otherwise found on or attached to the surface of the band with the timing marks also being attached on or embedded in the band. Such timing marks are utilized in the control circuitry of printing control means wherein storage means, tracking means and timing comparison means operate with the input data to fire the hammers at the precise times to print the desired data on the record media.
A common printing format includes spacing of the imprinted characters at 1/10 inch for printing all the characters in a line of print. Since the characters in a line of print are aligned with the print hammers for a short period of time, it should be realized that the print hammers must be fired at the exact instant the proper characters appear at the print positions.
Representative prior art in the area of band printers include U.S. Pat. No. 2,993,437, issued July 25, 1961, to F. M. Demer et al., which discloses high speed printer apparatus operable on a subcycle basis by spacing characters on the type chain so that only certain separate print positions along the print line will have characters aligned therewith at any one time. Intermediate print positions will subsequently have other characters aligned therewith and printing at such print positions cannot occur until subsequent subcycles occur. The number of subcycles necessary for aligning the different character fonts with every print position depends on the spacing ratio between the characters and the adjacent print positions. The characters are placed so that three characters span four print positions or every other character is aligned at every third hammer position to give a typed spacing of 11/2 pitch. Sequences of subcycles are repeated until one set of characters has been aligned with every print station.
U.S. Pat. No. 3,012,499 issued Dec. 12, 1961, to S. Amada, discloses a high speed printing system for increasing the number of words or letters printed in a line to increase the quality of words or letters recorded in a unit of type. The type characters are arranged in a plurality of rows on the type belt and the type hammers are arranged with certain offset rows and with selected hammers being shifted for operation at other rows.
U.S. Pat. No. 3,697,958 issued Oct. 10, 1972, to J. J. Larew, discloses a font selecting system including a method for shifting from a first to a second font of printing data responsive to remote signals. The apparatus is operative to selectively print characters from one of a plurality of fonts in response to signals identifying the font and the characters and includes means for storing the character data, font selection means responsive to the font selection signals to modify the stored data, means for generating data representative of characters and their positions and means for comparing the stored data with the generated data to control printing of the desired characters.
U.S. Pat. No. 3,699,884 issued Oct. 24, 1972, to L. W. Marsh, Jr. et al. discloses control for a chain printer including character generation accomplished where type spacing is greater than print position spacing by tracking the scan of the memory with a single tracking or address counter and using the output thereof to control the character generation and comparison functions. The phase counter arrests the advance of the character generator when predetermined counts are exhibited by the tracking counter and maintain the character generation sequence. Generation of beginning of the font or index synchronizing pulses regardless of the length of the font is accomplished by deriving a sequence of pulses from a code disc and using the moving type character carrier to gate the proper pulse to control circuits in accordance with the length of the font on the carrier.
U.S. Pat. No. 3,795,186 issued Mar. 5, 1974, to R. H. Curtiss et al. discloses a high speed printer wherein the type carrier includes a number of type fonts thereon and co-acts with a number of sets of hammers, one hammer for each character position in a line and a hammer driver for each set of hammers, the hammers being time shared among those of a set. The characters from the type carrier are spaced from one another at a distance greater than the spacing between character positions on the print medium.
And, U.S. Pat. No. 3,952,648 issued Apr. 27, 1976, to J. Sery et al. discloses a character printing device wherein the spacing between characters on the belt is greater than the spacing between hammers so that during one cycle in which all characters of a set have passed a given hammer, there are a number of scan cycles in which a number of different hammers, that is, one from each set, are aligned with characters a given number of successive subscan times where the number of scan cycles is equal to the number of characters in a set. The designation of a particular scan cycle for any given hammer defines the character which will be struck by that hammer during that subscan. The printing system detects the identities that can appear between the data originating from a unit to detect coincidence of characters and striking units and from a memory to record data concerning the characters to be printed and their positions and then control the striking units. The system also includes a reference memory containing data relating to the coincidences of characters and striking units for one of a series of characters, the coincidences appearing in the course of an initial scan period representing the time interval separating two successive coincidences of characters with a single striking unit.